1. Field of the Invention
The present invention is related to a light guide for endoscopes, that is, a light guide that propagates light therethrough such that portions which are observed with an endoscope are illuminated.
2. Description of the Related Art
Conventionally, endoscopes are in wide use to observe and perform surgical procedures on portions within body cavities of humans. Flexible light guides for illuminating the observed portions of subjects are employed in these endoscopes. Note that in cases that surgical procedures are performed on portions, observation thereof is necessary. Therefore, portions on which surgical procedures are performed will also be referred to as “observed portions” in the present specification.
At least a portion of this type of light guide is generally constituted by a plurality of thin multi mode optical fibers which are bundled, to impart flexibility thereto. Japanese Unexamined Patent Publication No. 6 (1994)-296584 discloses an example of a light guide for endoscopes configured in this manner. This light guide for endoscopes receives illuminating light beam, by the illuminating light beam being emitted from an illuminating light source, focused, then irradiated on a first end facet of the light guide. The illuminating light beam propagates through the light guide and is emitted from a second end facet to illuminate an observed portion.
Administering glass forming at the light input portions and the light output portions of conventional light guides for endoscopes such that they are maximally densely filled, that is, the spaces among the optical fibers at these portions are minimal, is being considered. Glass forming is a technique in which external pressure is applied to a plurality of bundled multi mode optical fibers while heating them at temperatures less than or equal to a glass softening temperature so as to densely assemble the optical fibers.
FIG. 10 is a sectional diagram that illustrates a maximally densely filled structure formed in the manner described above. FIG. 11 is a diagram that illustrates an example of a light guide 5 for endoscopes that employs the maximally densely filled structure. In FIG. 10 and FIG. 11, reference numeral 11 denotes a plurality of multi mode optical fibers, and reference number 12 denotes a filling adhesive for fixing the multimode optical fibers 11 in a bundled state such that the maximally densely filled structures can function as connector portions. Reference numeral 3 of FIG. 11 denotes a reinforcing structure for reinforcing the portion onto which glass forming has been administered. The reinforcing structure 3 is provided, because the multi mode optical fibers 11 become frangible by applying heat and pressure as described above. Reference numeral 6 of FIG. 11 denotes an illuminating light source for emitting an illuminating light beam 7, reference numeral 8 denotes a focusing optical system for focusing the illuminating light beam 7 and causing it to enter the plurality of multimode optical fibers 11 from a side towards first facets (light input facets) thereof, and reference numeral 9 denotes an optical element which is provided in close contact with the second facets (light output facets) of the multi mode optical fibers 11.
There is a problem that first facets that function as light input portions and second facets that function as light output portions of conventional light guides for endoscopes, which are constituted by bundling a plurality of thin optical fibers together, are easily damaged.
In addition, it is desirable for the light output portions of light guides for endoscopes to have greater numerical apertures, such that illuminating light beams can be emitted with a wide angle of spread to illuminate greater areas of observed portions. Meanwhile, it is also desirable for the light input facets of the light guides to have greater numerical apertures, such that the light receiving angle thereof (corresponding to the angle of spread at the light output facet) becomes great to increase the utilization efficiency of the illuminating light beams. There is still room for improvement in conventional light guides for endoscopes in the point of increasing the numerical apertures of the light input portions and the light output portions.